In 1944 Knutson described a formula for estimating age specific DMFT means from the percent of individuals in the age group having one or more decayed, missing or filled teeth. This formula was evaluated for both different age ranges, and for different allowable maximum percentages using 14 NCP data sets. The method of weighted least squares was used to fit the formula. Results indicate that restrictions of age range, and maximum percent of individuals with one or more DMF teeth, are necessary before applying the formula. It was determined that for K equals 100, and B equals 0.542 the formula could be applied to age groups in the 5-11 year old range which also had not more than 70% of the children with one or more DMFT.